1. Field of the Invention
This invention relates to a bladder control mechanism of a tire vulcanizer.
2. Description of the Prior Art
A conventional tire vulcanizer of the type using a bladder will be described with reference to FIGS. 7 and 8. In these drawings, T designates a tire under vulcanization, M a metal mold comprising an upper mold half Ma and a lower mold half Mb, and Pa and Pb upper and lower platens for heating the metal mold M from the upper and lower sides. Reference numeral 1 designates a body frame, 2 a bladder control mechanism, 3 an upper central mechanism including a known chuck mechanism, and 4 a pressure cylinder.
The bladder control mechanism 2 comprises a bladder receiving barrel 11 suspended from the lower platen Pb, a lower ring 12 slidable along the inner surface of the bladder receiving barrel 11, an upper ring 13 slidable along the inner surface of the lower ring 12, a center post 14 air-tightly slidable inside a central section of the upper ring 12, a center-post lifting cylinder 17 secured to a bottom plate of the bladder receiving barrel 11 and whose piston rod 17a is secured at its end to the lower end of the center post 14, a sleeve 16 secured to the lower face of the lower ring 12, a bladder clamping cylinder 18 secured to the lower end of the sleeve 16 and whose piston rod 18a is secured at its end to the lower end of the center-post lifting cylinder 17, a bladder gripping bowl 21 secured to the upper end of the center post 14 via a split ring 19 and a split-ring holder 20, and a bladder holder 22 detachably attached to the bladder gripping bowl 21 by a bolt 23.
The upper ring 13 is provided with nozzles 13a and 13b through which a heating medium of high temperature and high pressure is injected into and ejected from a bladder B. The upper edge of the lower ring 12 and of the upper ring 13 define a recess in which a lower edge portion of the bladder B is received and gripped. When the upper ring 13 is moved upwards relative to the lower ring 12 by operating the bladder clamping cylinder 18, the lower edge portion of the bladder B is released from the gripped state; on the other hand, when it is moved downwards, the lower edge portion is gripped.
The conventional tire vulcanizer of the type using a bladder as shown in FIGS. 7 and 8 has the following problems.
(1) During tire vulcanization, the bladder B expands; as a result, an internal force acts on the gripped portion such that the bladder B elongates radially, and due to creep, there is a tendency for the thickness to decrease as time elapses. Therefore, since an upper edge portion of the bladder B is gripped by bolting, it is necessary to stop the machine periodically to perform re-bolting or re-tightening. Especially after a new bladder B has been substituted, re-tightening must be performed frequently.
(2) The bladder B must be replaced not only when the tire size is changed but also when three or four days have passed even where the tire size is unchanged. However, it is not easy to detach the bladder holder 22 because the temperature therearound is as high as 100.degree. C., and there is a bonded portion where a sealing compound has been applied in order to solve the problem (1) above. Thus, the exchanging of bladders must be made manually under bad conditions which imposes severe work on workers and demands a large amount of time.
(3) The two problems above have been solved substantially in relation to the lower edge portion of the bladder B. However, they have not yet been solved in relation to the upper edge portion because of limitations relating to space, temperature, etc.